One interesting plot could be a magical duel between Harry and Snape where they both use unexpected spells. Harry might draw on some newfound knowledge from an ancient magic book, while Snape uses his years of experience and dark arts knowledge in a creative way.
It really depends on the writer. Some might make Harry more powerful because he has the power of love and friendship on his side, which is a strong force in the wizarding world. Also, he has his own natural talent for magic.
One great Snape vs Voldemort fanfiction is 'The Dark Mark's Secret'. It delves into Snape's complex relationship with Voldemort. Snape is constantly in a precarious position, having to play the double agent. The story shows how he uses his wits against Voldemort's brute power. Another one is 'Snape's Hidden Alliances'. It focuses on how Snape manages to outmaneuver Voldemort in some crucial situations. The characterizations are really well - done in both of these, making them engaging reads.
Another theme is loyalty. They both have deep loyalty to Hogwarts but express it in different ways. Snape's loyalty is complex and often misunderstood, while McGonagall's is more straightforward. Fanfictions explore how these different loyalties can cause friction between them. In a lot of these stories, their loyalty also brings them together in times of crisis. For instance, when Voldemort's forces threaten the school, they have to find a way to cooperate despite their differences. This exploration of loyalty makes the fanfictions really engaging.
In some fanfictions, their rivalry might be explored in the context of the Hogwarts Houses. For example, McGonagall being a proud Gryffindor and Snape a Slytherin. There could be a story where they have to resolve a conflict between the two Houses, and their different approaches to the situation create a lot of tension and drama.
In some fanfictions, Snape might use his advanced knowledge of potions to brew a special healing elixir for Harry. He could also use his magic skills, like a complex spell specifically designed to mend Harry's wounds, whether they are physical or emotional.
In some fanfics, Snape might punish Harry because of his perceived insolence in class. Harry has a rebellious streak, and Snape, being strict, wouldn't tolerate any behavior that he deems disrespectful to his authority as a teacher.
Perhaps it's related to Harry's association with his father, James Potter. Snape had a long - standing grudge against James, and seeing Harry might bring back those bitter memories. So, whenever Harry does something that reminds Snape of James, like being overly confident or a bit of a troublemaker, he yells at him.
In some fanfics, Snape might hurt Harry out of his long - held grudges. Snape was in love with Harry's mother, Lily, and Harry being a reminder of James, who bullied Snape in school, could trigger his negative emotions. Also, Snape's loyalty to Voldemort in the earlier days in some fan - created scenarios might lead him to target Harry, who was seen as a threat to Voldemort's plans.
The main thing that makes Snape vs Voldemort fanfiction interesting is the contrast between the two characters. Snape is complex, with his own motives and a hidden side. Voldemort is pure evil. So when they interact, there are always mind games and power plays. For example, Snape has to constantly deceive Voldemort, and the tension this creates is exciting.